Yes, it affects all sources of healing, but keep in mind that it’s relative to the amount of healing, not the total HP.
In other words, these things are totally different:
- 10% Healing = heals for 10% of total HP
- 10% Healing Bonus = heals for 10% of the amount of healing
So a 10% Healing Bonus applied to a 10% Healing would actually only increase the Healing by 1% of the HP.
For another example, if you have a 15% Healing Bonus from a Troop, and fire Rigard’s 42% Healing, the Hero with the Healing Bonus will get the equivalent of 48.3% Healing, NOT 57%.
So the 2% Healing Bonuses from the Talent Grid are pretty paltry — they’d only increase Rigard’s Healing from 46% to 47%, Kiril’s from 30% to 30.6%, and Costumed Hawkmoon’s from 459 HP to 468 HP, for instance.